I’m writing this post as a “passing of the baton” so hopefully someone can start this project with a LOT of legwork and questions answered—which might motivate them to actually execute the project. I didn’t do it because it was death by 1000 cuts, I spent a LOT of time scoping this and I hadn’t even done anything yet! I just couldn't justify the time and money at this stage of my life, but hopefully someone else can and I hope this proves incredibly useful to them.
First off, the idea seems great because the A750 was put behind the 1HDFTE in some HDJ100’s. So, a swap should be pretty simple, right? There are a few elements to this which I’ll discuss in depth that all need properly addressed:
You’ll need to source a diesel torque converter from HDJ100/101 that had an A750 behind it. Ideally you want to source it from a later HDJ100, I read that the initial 2001 model had known TC problems which was revised I believe starting in 2003--I think this is why all the transmission P/Ns change then.
BELLHOUSING
Looking at the bolt pattern, I actually think the A442 bellhousing will mount to the A750—minus a few extra bolts that look like beefed up support/attachment. But the best way to do this is to source a whole A750 transmission from an HDJ100/101 for case reasons I’ll describe below. It’s handy to know that the difference between UZJ vs. HDJ bellhousing is that the UZJ has the starter at the top (12-o-clock) vs. the HDJ which has it at the ~3-o-clock position. Transmissions from the two vehicles are not directly interchangeable.
TRANSMISSION-SHIFTER LOCATION:
The original idea I had was to use a US-sourced A750 because they’re everywhere. But it turns out that using a US-sourced A750 is difficult because the actual transmission housing is different which moves the location of the transfer shifter back a few inches. It's on the rear casing instead of on the transmission itself. Here's a photo of a US-based A750, it looks like many other rigs share the same transmission housing P/N as UZJ100s:
Compare this to the HDJ100 A750 version, the rear casing doesn't have any feature to accept the shifter and it's built into the housing instead:
This is exactly like the HDJ81 A442:
This would explain why the rear casing P/Ns are different between HDJ and UZJ models even though they bolt to the same transmission and transfer. Keeping this in the same location is important as it makes life a lot easier on the console side, which I’ll discuss later.
TRANSMISSION- REAR CASING & SHAFTS:
The only other difference I've been able to find is that the input and output shafts are different P/Ns although I'm not sure what the actual differences are internally or if those differences really matter to the function of the transmission in a diesel vs. gasser. There might be other differences which is why getting a diesel transmission is the best idea (see my comments in ELECTRONICS for why this might be important). I'm pretty sure the external aspect of the input and output shaft is identical between HDJ100 and UZJ100. The output shafts and rear casings from various other US-based vehicle versions of the A750 will not be even remotely correct and it takes tearing apart the transmission to swap it out. So, if you’re planning on getting a US transmission and rebuilding it anyway this isn’t such a big deal—but you’ll still need a new rear case and output shaft which ain’t cheap. The A750 from an HDJ should bolt onto the HF2A transfer currently behind the A442 in HDJ81's.
TRANSMISSION-A NOTE ABOUT PART NUMBERS:
For some reason it appears as though Toyota/Aisin quit putting ID plates on the newer transmissions. Instead there are these little paper stickers--the P/Ns on them can be deceiving and not entirely correct, so be very careful when buying a transmission after it’s been removed from the donor vehicle. The P/N for the transmission you want is 35000-60A10, however other’s might work that don’t match that P/N. You really need to get good at recognizing the key features of the correct A750 which I’ve outlined in my photos above.
At the very end of this I realized that the funny little arm that the shifter connects to on the side of the transmission has a P/N stamped on it which could be used to authoritatively determine exactly which group of cars this transmission came from. This was also partly terrifying, there's like 8 different versions of this stupid thing for unknowable reasons. Will that pose a problem on a swap? Who knows.
CROSS MEMBER & DRIVESHAFTS:
I’m pretty sure the crossmember can stay in the same spot although height might be an issue. On my A442 the main tranny case measured 23 3/4" and the rear housing measured 4 3/4". On the HDJ100 transmission the main case measured the same but the rear housing measured slightly shorter at 4 3/8”. I THINK this is just measurement error on my A442 from doing it on-rig at a spot where I don’t have a perfectly straight surface to measure and likely they are identical. I’ll update this when I measure at the same spot with an off-rig A442.
ELECTRONICS/TCM
I spoke at length with Jono @ Wholesale Automatics about his conversion (the writeup on their website) and the others he’s done (Note: They’ve NEVER done an A442-to-A750, only manual-to-auto).
The electronics in the US are purchased directly through HGM, the manufacturer. I talked to them on the phone, they said the A750 was a PITA and only Wholesale programs them. Compare this to, for example, some online reviews of their GM installs that make it look so simple. But Jono has programmed these things remotely before so it’s not a huge deal to do. Basically, the more your transmission is worn or away from stock, the harder it will be to program….so if you get a gasser from a 4Runner as your donor you might end up with programming difficulty--who knows? He has a default config file that comes with the purchase from HGM, any tweaking beyond that is billed. For budgetary purposes if you plan on an extra ~$1000 in tweaking you should be safe. It could take two weeks of this to dial in to your liking.
You need speedometer and tachometer digital inputs in addition to TPS. We didn’t discuss what or how this occurs, although the website article on his conversion mentions difficulties with the tachometer. So, no matter what it’s a thing that needs dealt with.
SHIFTER
I’m saving the best for last because this is the real kick in the nuts. This is just what it says online in the HGM product selector: HDJ “gate” vs. Prado “tiptronic”. But there’s some very, very important details about this.
Obviously the cheapest/easiest route would be to use the mechanical linkage that came with the HDJ’s when they used this transmission, that’s the “gate” shifter. The problem on the 80 series is that it doesn’t really land quite right, the floor is seriously curved there and there’s not a good place to mount the shifter. It would basically sit as far as I can tell pretty close to the middle, between the transfer lever and the center fridge or maybe right on the transfer lever. There is probably not room without moving the transfer shifter (see console discussion below) = more parts and money.
Sure you can move the linkage itself but how much will this screw up the proper shifting? You’ll probably end up putting the transmission in place a ton of times trying to get the linkage just right and troubleshooting interferences. Total nightmare. By the way these linkage connection arms on the transmission itself are all unique and have different P/Ns depending on specific model, so I assume the exact geometry is probably fairly important.
In comparison, the great thing about the Prado 150 tiptronic shifter is that you can literally put it anywhere because it’s cable-driven—no linkages! Wherever you want it, drill a hole and run the cable and you’re done! So, yeah, why wouldn’t you do this? Cost. It turns out the Prado shifter uses electronic control for downshift on a few gears whereas the HDJ shifter uses mechanical control. Therefore, for these gears to work properly in the A750 you need a new valve body. Ugh!!!! They also seem more difficult to source and are quite expensive as an entire set new.
So you can hope that you can get the HDJ mechanical linkage to work properly without a week of work setting your transmission over and over again—and have look good wherever it lands because you don’t have a lot of choices—or spend a few more grand on the Prado shifter but simply put it where it looks/feels good in the rig.
CONSOLE
The console from Wholesale is the entire shifter/center console in one so it replaces the fridge. That makes it a no-go to me. Note the location of the transfer shifter in the middle, this probably matches the stock HDJ81 location:
So, needing a console opens an entire can of worms that needs solved. Delta makes a console for an 80 series but it would obviously require significant modification (I was hoping the large sum of money I’ve spent with him over the winter and the idea of this amazing upgrade might motivate him to help me with a custom console). No matter what shifter you go with, they’re much taller. Basically the console ends up at the bottom of the heater controls. Jono has his own unique console, see how tall it is:
Note the location of his transfer shifter. This is accomplished by using the transfer lever linkage off a late-90’s HDJ81 manual transmission rig—it’s what his rig came with. An auto doesn't have this. This would likely be a requirement if you were going to try and use the HDJ100 shifter as it should likely fall right where the stock transfer lever sits on an auto. So, more parts to source, and money, no matter how you go.
COST
Jono told me to estimate $15k and if it came in less, great. I think that's probably a safe budgetary estimate if you do all the work yourself. Here’s my actual cost estimates based upon real-world prices I could find online:
Alternatively, you could go with the Prado shifter for maybe $1000 in used parts but you also need to upgrade the valve body for the electronic control so that’s another ~$1500. It probably saves maybe $500 in parts from the HDJ gate shifter option, so this is maybe a $2k increase in overall price but a hell of a lot easier. Now we’re at $8800 and the transmission is still sitting on another continent. But again it still needs to be fit together with a new-from-scratch console.
Note that this quickly gets very expensive if you need to rebuild the transmission for another $4k! Part of the reason this was even remotely approachable is because I found that NOS transmission! The more I looked into this the more little details there were to attend to, so I don’t consider this cost estimate to be that realistic. This is death by a thousand cuts and many thousands of dollars for sure. Maybe $10k, maybe…..with a brand-new transmission at used prices, doing all the labor myself.
CONCLUSION
I hope that someone can take this information and run with it and see this project through. IT WOULD BE SUCH A RAD RIG!!!! But simply scoping this project was enough work to make me realize that I didn’t want to spend $10k+ to create 3-6 weeks of intense labor for myself hacking this together. I mean, it takes a hell of a lot of frustrated driving to make that worth the effort. I’d rather use the money saved on a “simple” A442 rebuild to drive my slow, lame-shifting butt down to Baja to sit in the beach for two months!
Useful links:
Ebay listing for the NOS HDJ100 A750 transmission, still for sale
You might be able to score a rebuilt one here in Europe, the prices seem reasonable
Used car parts in Australia....note that auto's seem very hard to find
This is a Russian search engine that is GREAT for getting photos, they seem very diligent about posting parts by Toyota P/N
First off, the idea seems great because the A750 was put behind the 1HDFTE in some HDJ100’s. So, a swap should be pretty simple, right? There are a few elements to this which I’ll discuss in depth that all need properly addressed:
- Torque Converter
- Bellhousing
- Transmission
- Rear Casing & Output Shaft
- Crossmember & Driveshafts
- Electronics/TCM
- Console/Shifter
- Cost
You’ll need to source a diesel torque converter from HDJ100/101 that had an A750 behind it. Ideally you want to source it from a later HDJ100, I read that the initial 2001 model had known TC problems which was revised I believe starting in 2003--I think this is why all the transmission P/Ns change then.
BELLHOUSING
Looking at the bolt pattern, I actually think the A442 bellhousing will mount to the A750—minus a few extra bolts that look like beefed up support/attachment. But the best way to do this is to source a whole A750 transmission from an HDJ100/101 for case reasons I’ll describe below. It’s handy to know that the difference between UZJ vs. HDJ bellhousing is that the UZJ has the starter at the top (12-o-clock) vs. the HDJ which has it at the ~3-o-clock position. Transmissions from the two vehicles are not directly interchangeable.
TRANSMISSION-SHIFTER LOCATION:
The original idea I had was to use a US-sourced A750 because they’re everywhere. But it turns out that using a US-sourced A750 is difficult because the actual transmission housing is different which moves the location of the transfer shifter back a few inches. It's on the rear casing instead of on the transmission itself. Here's a photo of a US-based A750, it looks like many other rigs share the same transmission housing P/N as UZJ100s:
Compare this to the HDJ100 A750 version, the rear casing doesn't have any feature to accept the shifter and it's built into the housing instead:
This is exactly like the HDJ81 A442:
This would explain why the rear casing P/Ns are different between HDJ and UZJ models even though they bolt to the same transmission and transfer. Keeping this in the same location is important as it makes life a lot easier on the console side, which I’ll discuss later.
TRANSMISSION- REAR CASING & SHAFTS:
The only other difference I've been able to find is that the input and output shafts are different P/Ns although I'm not sure what the actual differences are internally or if those differences really matter to the function of the transmission in a diesel vs. gasser. There might be other differences which is why getting a diesel transmission is the best idea (see my comments in ELECTRONICS for why this might be important). I'm pretty sure the external aspect of the input and output shaft is identical between HDJ100 and UZJ100. The output shafts and rear casings from various other US-based vehicle versions of the A750 will not be even remotely correct and it takes tearing apart the transmission to swap it out. So, if you’re planning on getting a US transmission and rebuilding it anyway this isn’t such a big deal—but you’ll still need a new rear case and output shaft which ain’t cheap. The A750 from an HDJ should bolt onto the HF2A transfer currently behind the A442 in HDJ81's.
TRANSMISSION-A NOTE ABOUT PART NUMBERS:
For some reason it appears as though Toyota/Aisin quit putting ID plates on the newer transmissions. Instead there are these little paper stickers--the P/Ns on them can be deceiving and not entirely correct, so be very careful when buying a transmission after it’s been removed from the donor vehicle. The P/N for the transmission you want is 35000-60A10, however other’s might work that don’t match that P/N. You really need to get good at recognizing the key features of the correct A750 which I’ve outlined in my photos above.
At the very end of this I realized that the funny little arm that the shifter connects to on the side of the transmission has a P/N stamped on it which could be used to authoritatively determine exactly which group of cars this transmission came from. This was also partly terrifying, there's like 8 different versions of this stupid thing for unknowable reasons. Will that pose a problem on a swap? Who knows.
CROSS MEMBER & DRIVESHAFTS:
I’m pretty sure the crossmember can stay in the same spot although height might be an issue. On my A442 the main tranny case measured 23 3/4" and the rear housing measured 4 3/4". On the HDJ100 transmission the main case measured the same but the rear housing measured slightly shorter at 4 3/8”. I THINK this is just measurement error on my A442 from doing it on-rig at a spot where I don’t have a perfectly straight surface to measure and likely they are identical. I’ll update this when I measure at the same spot with an off-rig A442.
ELECTRONICS/TCM
I spoke at length with Jono @ Wholesale Automatics about his conversion (the writeup on their website) and the others he’s done (Note: They’ve NEVER done an A442-to-A750, only manual-to-auto).
The electronics in the US are purchased directly through HGM, the manufacturer. I talked to them on the phone, they said the A750 was a PITA and only Wholesale programs them. Compare this to, for example, some online reviews of their GM installs that make it look so simple. But Jono has programmed these things remotely before so it’s not a huge deal to do. Basically, the more your transmission is worn or away from stock, the harder it will be to program….so if you get a gasser from a 4Runner as your donor you might end up with programming difficulty--who knows? He has a default config file that comes with the purchase from HGM, any tweaking beyond that is billed. For budgetary purposes if you plan on an extra ~$1000 in tweaking you should be safe. It could take two weeks of this to dial in to your liking.
You need speedometer and tachometer digital inputs in addition to TPS. We didn’t discuss what or how this occurs, although the website article on his conversion mentions difficulties with the tachometer. So, no matter what it’s a thing that needs dealt with.
SHIFTER
I’m saving the best for last because this is the real kick in the nuts. This is just what it says online in the HGM product selector: HDJ “gate” vs. Prado “tiptronic”. But there’s some very, very important details about this.
Obviously the cheapest/easiest route would be to use the mechanical linkage that came with the HDJ’s when they used this transmission, that’s the “gate” shifter. The problem on the 80 series is that it doesn’t really land quite right, the floor is seriously curved there and there’s not a good place to mount the shifter. It would basically sit as far as I can tell pretty close to the middle, between the transfer lever and the center fridge or maybe right on the transfer lever. There is probably not room without moving the transfer shifter (see console discussion below) = more parts and money.
Sure you can move the linkage itself but how much will this screw up the proper shifting? You’ll probably end up putting the transmission in place a ton of times trying to get the linkage just right and troubleshooting interferences. Total nightmare. By the way these linkage connection arms on the transmission itself are all unique and have different P/Ns depending on specific model, so I assume the exact geometry is probably fairly important.
In comparison, the great thing about the Prado 150 tiptronic shifter is that you can literally put it anywhere because it’s cable-driven—no linkages! Wherever you want it, drill a hole and run the cable and you’re done! So, yeah, why wouldn’t you do this? Cost. It turns out the Prado shifter uses electronic control for downshift on a few gears whereas the HDJ shifter uses mechanical control. Therefore, for these gears to work properly in the A750 you need a new valve body. Ugh!!!! They also seem more difficult to source and are quite expensive as an entire set new.
So you can hope that you can get the HDJ mechanical linkage to work properly without a week of work setting your transmission over and over again—and have look good wherever it lands because you don’t have a lot of choices—or spend a few more grand on the Prado shifter but simply put it where it looks/feels good in the rig.
CONSOLE
The console from Wholesale is the entire shifter/center console in one so it replaces the fridge. That makes it a no-go to me. Note the location of the transfer shifter in the middle, this probably matches the stock HDJ81 location:
So, needing a console opens an entire can of worms that needs solved. Delta makes a console for an 80 series but it would obviously require significant modification (I was hoping the large sum of money I’ve spent with him over the winter and the idea of this amazing upgrade might motivate him to help me with a custom console). No matter what shifter you go with, they’re much taller. Basically the console ends up at the bottom of the heater controls. Jono has his own unique console, see how tall it is:
Note the location of his transfer shifter. This is accomplished by using the transfer lever linkage off a late-90’s HDJ81 manual transmission rig—it’s what his rig came with. An auto doesn't have this. This would likely be a requirement if you were going to try and use the HDJ100 shifter as it should likely fall right where the stock transfer lever sits on an auto. So, more parts to source, and money, no matter how you go.
COST
Jono told me to estimate $15k and if it came in less, great. I think that's probably a safe budgetary estimate if you do all the work yourself. Here’s my actual cost estimates based upon real-world prices I could find online:
- Electronics/TCM from HGM: $1800
- Console: $1000 (total guess, never talked to anyone about this)
- Used torque converter + HDJ100 gate shifter + HDJ81 manual transfer shifter linkage : $1000 (Thanks @Bardiya!)
- Converter Rebuild: $500
- A750 NOS: $2500+shipping. NOTE: This was a KILLER find and will likely never be replicated. I was quoted $1700 for a used HDJ A750 with torque converter (Thanks @Bardiya!) but it all needed shipped from UAE. If you go with a used transmission, you will likely pay for some of your savings in programming time!
Alternatively, you could go with the Prado shifter for maybe $1000 in used parts but you also need to upgrade the valve body for the electronic control so that’s another ~$1500. It probably saves maybe $500 in parts from the HDJ gate shifter option, so this is maybe a $2k increase in overall price but a hell of a lot easier. Now we’re at $8800 and the transmission is still sitting on another continent. But again it still needs to be fit together with a new-from-scratch console.
Note that this quickly gets very expensive if you need to rebuild the transmission for another $4k! Part of the reason this was even remotely approachable is because I found that NOS transmission! The more I looked into this the more little details there were to attend to, so I don’t consider this cost estimate to be that realistic. This is death by a thousand cuts and many thousands of dollars for sure. Maybe $10k, maybe…..with a brand-new transmission at used prices, doing all the labor myself.
CONCLUSION
I hope that someone can take this information and run with it and see this project through. IT WOULD BE SUCH A RAD RIG!!!! But simply scoping this project was enough work to make me realize that I didn’t want to spend $10k+ to create 3-6 weeks of intense labor for myself hacking this together. I mean, it takes a hell of a lot of frustrated driving to make that worth the effort. I’d rather use the money saved on a “simple” A442 rebuild to drive my slow, lame-shifting butt down to Baja to sit in the beach for two months!
Useful links:
Ebay listing for the NOS HDJ100 A750 transmission, still for sale
You might be able to score a rebuilt one here in Europe, the prices seem reasonable
Used car parts in Australia....note that auto's seem very hard to find
This is a Russian search engine that is GREAT for getting photos, they seem very diligent about posting parts by Toyota P/N
